Require Language In PostgreSQL Extension Control File

I'm developing a custom extension that uses plpythonu in several functions. I'd like to be able to require that plpythonu be installed in order to create my extension, but I don't see anything in the documentation about requiring a language via the control file. I tried adding plpythonu to the 'requires' statement in the control file but it looks for an extension named plpythonu rather than the language. Can this be done?